1. Field of the Invention
The present invention relates to an improvement of the output waveform in an inverter.
2. Description of the Prior Art
In the conventional pulse width modulation system, by turning on and off switches, the steps of an AC waveform are changed. Accordingly, low order harmonics are produced. In order to remove the low order harmonics, it is necessary to increase the filters and phases of the high-frequency modulation. A complicated power source apparatus is disadvantageously required.
In accordance with the invention, a pulse allocater for controlling a plurality of switches in a predetermined order (such as a ring counter) is provided whereby fine pulse width modulated waveforms are generated by controlling the progress and retrogress of the transposition order of the output from the pulse allocater. The control of the switches is performed to attain a fine control of the increase and the decrease of load current.